Abstract: A receiver in a frame based radio communication system includes a speech decoder of the source-filter type which is controlled by internal state variable updated on a frame by frame basis for modifying received filter parameters representing background sounds transmitted over a communication channel. The receiver detects frames containing transmission errors, decides whether a frame in which transmission errors have been detected is acceptable, and conceals the detected transmission errors by restricting updating of at least one of the internal state variables if the detected frame is declared non-acceptable.

Abstract: A receiver in a frame based radio communication system includes a speech decoder of the source-filter type which is controlled by internal state variables updated on a frame by frame basis for modifying received filter defining parameters representing background sounds transmitted over a communication channel. The receiver detects frame loss and conceals the effects of frame loss by restricting updating of at least one of the internal state variables.

Abstract: A discriminator discriminates between stationary and non-stationary signals. The energy E(T.sub.i) of the input signal is calculated in a number of windows T.sub.i. These energy values are stored in a buffer, and from these stored values a test variable V.sub.T is calculated. This test variable comprises the ratio between the maximum energy value and the minimum energy value in the buffer. Finally, the test variable is tested against a stationarity limit .gamma.. If the test variable exceeds this limit the input signal is considered non-stationary. This discrimination is especially useful for discriminating between stationary and non-stationary background sounds in a mobile radio communication system.

Abstract: A method and apparatus for improving the decoding of audio signals is disclosed. In a receiver of a frame based radio communication system, rejected frames are concealed according to a first algorithm if the last accepted frame was a speech frame and according to a second algorithm if the last accepted frame was a frame containing background sounds.